Cell cycle signaling

The eukaryotic cell cycle is driven by CDK–cyclin pairs and guarded by the Rb–E2F switch, replication licensing, DNA-damage responses, and the spindle assembly checkpoint. Mitogens (RTK–Ras–ERK, PI3K/Akt, etc.) and stress cues set the G1 restriction point and the G2/M transition; cancer often shows cyclin/CDK amplification, CKI loss, or checkpoint bypass—making the cycle a central space for antibody readouts and CDK4/6-class therapeutics.

1. Key targets

CDK–cyclin engine

  • G1 / G1–S

    Cyclin D–CDK4/6 integrates mitogens; Cyclin E–CDK2 promotes licensing and S entry.

  • S / G2

    Cyclin A–CDK2 supports replication; Cyclin A/B–CDK1 drives mitosis (MPF).

  • CKIs & regulatory subunits

    INK4 (p16) inhibits CDK4/6; Cip/Kip (p21/p27) broadly inhibit pairs; E3s such as Skp2 tune cyclin turnover.

Rb – E2F

  • Hypo-p-Rb restrains E2F-dependent S-phase genes
  • CDK progressive p-Rb releases E2F1–3 for PCNA/MCM/TS programs

Mitosis & exit

  • Aurora A/B, PLK1, CDC25s tune centrosomes and CDK1 activation
  • APC/C–Cdc20/Cdh1 targets securin and Cyclin B for anaphase/exit

2. Suggested experimental readouts

p-Rb epitopes differ by clone; Ki-67 is a proliferation index—interpret kinetics; pair EdU/BrdU with cyclin IF when possible.

  • p-Rb (Ser807/811, etc.) with total Rb; Cyclins D1, E, A, B1
  • p21, p27, p16; phospho-CDK when clone-validated
  • Ki-67, PCNA, MCM2/5, Geminin (S-phase dynamics)
  • p-Histone H3 (Ser10)—mitosis; gamma-H2AX—stress/DDR
  • p-CHK1 (Ser345), p-CHK2 (Thr68)—checkpoint activation

3. Major checkpoints & sensors (overview)

PhaseCore questionExample nodes
G1 / restrictionCommit to replication and S-phase transcription?Cyclin D–CDK4/6, Cyclin E–CDK2, Rb, E2F, p16/p21/p27
Intra-S / stressFork integrity under stress?ATR–CHK1, RPA, gamma-H2AX, PCNA
G2 / MReplication complete with tolerable damage?WEE1, CDC25, Cyclin B–CDK1, CHK1/2
SACChromosomes bioriented on the spindle?Mad2, BubR1, Cdc20–APC/C

4. Cancer, CDK4/6 inhibitors & resistance

  • CDK4/6 + endocrine / targeted partners: HR+ breast cancer often pairs CDK4/6i with endocrine/targeted partners—annotate Rb status and Cyclin E1 bypass cues.
  • p16 / CDKN2A loss: weakens CDK4/6i dependency; MAPK/CDK2 compensation appears in many models.
  • Replication stress & DDR: ATR/CHK1 couples tightly to cycle biology—pair synchronization strategies in SL/CRT studies.

Cell cycle–related antibodies (curated)

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5. Product lines & on-site search

Primary & phospho antibodies

Cyclins D1/E/A/B, p-Rb, CDK2/4/6, phospho-CDK, E2F1, p21/p27/p16, Ki-67, PCNA, PLK1, Aurora A/B, gamma-H2AX, p-CHK1/2—WB/IHC/IF/FC per datasheet.

Functional reagents & proliferation readouts

EdU/BrdU kits, PI/RNase cell-cycle flow panels—availability-dependent.

6. Inhibitors & tool compounds (summary)

Clinical agents are prescription drugs; for research, follow datasheets, ethics, and off-target panels.

Palbociclib / Ribociclib / Abemaciclib

CDK4/6; labels vary by region/indication.

Roscovitine (Seliciclib)

Multi-CDK tool (CDK2/1/5/9 bias—check profiling).

Flavopiridol (Alvocidib)

Broad CDK / transcriptional effects—toxicity context.

RO-3306 / BI2536

CDK1 or PLK1 tools; mitotic synchronization.

AZD1775 (Adavosertib)

WEE1 inhibitor; G2/M checkpoint studies.

VX-970 (Berzosertib)

ATR inhibitor; pair with RS/DDR readouts.

7. Pathway schematic

Phases & checkpoints (schematic)
Cell cycle pathway schematic
Legend
  1. G1: Cyclin D–CDK4/6 integrates growth cues
  2. S: forks with Cyclin A–CDK2
  3. G2/M: Wee1–Cdc25 and Cyclin B–CDK1
  4. Rb–E2F plus CKIs set the G1/S threshold

8. Pathway biology overview

The cycle is not a uniform clock but an ordered sequence of switches: Rb–E2F, APC/C, and licensing modules create nonlinear thresholds so cells can reversibly—or irreversibly—respond to nutrients, DNA lesions, and kinetochore attachment. Development and regeneration demand precise CDK phasing; senescence and cancer often reflect checkpoint fatigue or cyclin/CDK hyperactivation.

  • Quiescence/exit: low CDK, CKI induction, p53 context
  • Polyploidy/endoreduplication: CDK–APC imbalance readouts

9. Related pathways on this site

MAPK/ERKTGF-β/SmadPI3K/Akt/mTORApoptosisWnt/β-cateninJAK-STATNF-κBReceptor tyrosine kinaseAngiogenesisInflammation

10. External databases & modification resources

11. References

Cycle engine & cancer

  • • Malumbres M, Barbacid M. (2009). Cell cycle, CDKs and cancer: a changing paradigm. Nat Rev Cancer. 9(3):153-66.
  • • Hanahan D, Weinberg RA. (2011). Hallmarks of cancer: the next generation. Cell. 144(5):646-74.

Checkpoint concepts

  • • Hartwell LH, Weinert TA. (1989). Checkpoints: controls that ensure the order of cell cycle events. Science. 246(4930):629-34.
  • • Elledge SJ. (1996). Cell cycle checkpoints: preventing an identity crisis. Science. 274(5293):1664-72.